1. Field of the Invention
This invention relates to a logic level interlock device for use with an electric control device such as a contactor or relay.
2. Background Information and Description of the Prior Art
Industrial equipment that is operated electrically such as by a motor is usually regulated by a control device which may be a contactor or a relay having parts movable between two positions for opening and closing a circuit through the motor. Some electric control devices utilize auxiliary contact assemblies for separate interlocking functions in numerous variations. Conventionally, these auxiliary contact devices have been actuated by an actuating member connected to the electromagnetic operating means responsible for opening and closing the electric circuit through the contactor.
Electromechanical interlock devices have been known such as that provided in U.S. Pat. No. 4,309,683 which is owned by the assignee of the present invention. U.S. Pat. No. 4,309,683 provides an electric control device having an auxiliary contact device which includes a contact carrying structure that controls the contacts of the control device. When the electric control device is energized, the insulating contact carrier is pulled down bringing a set of movable contacts into electrical contact with a set of stationary contacts. The main contact carrier also controls an auxiliary contact carrier. The main contact carrier, by means of a slot which engages a protruding tab on the auxiliary contact carrier moves the auxiliary contact carrier downward which closes the contacts of the auxiliary contact device. When the control device is deenergized, the contact carrier moves upward to its normal position and this motion also causes the slots to carry the auxiliary contact carrier to its normal position.
The conventional auxiliary interlock devices such as that described above operate at the same high current and high voltages as the other components in the conventional electric control system. More recently, however, it is preferred to use microprocessors or other programmable logic controllers ("PLCs") for control of the contactor and motor assembly. It is necessary, therefore, that the interlock device for sensing whether the contactor is opened or closed generate a logic level signal of 5 volts or less. Such low voltage signals are not amenable to use with the conventional auxiliary contacts such as that described above. The low voltages can cause the contacts to oxidize. This can in turn result in unnecessary contact wear.
There remains a need for a device which can generate a logic level signal in response to the contactor or motor controller which will avoid the above mentioned problems of oxidation of contacts and early contact wear. In addition, there remains a need for a device which can operate with low level strobed circuits for position sensing such as on/off sensing in controlled feedback networks. There remains yet a further need for an interlock for use with contactors which provides signals for communication with microprocessors and other similar devices.